I liked the panel discussions, and the readings done by authors. I liked talking to whomever you sat next to/stood at the bar with, because you knew you had common interest, and you met some great people. I didn't like 2 hour lunches, and I didn't like the way some cliques always formed, of the same writers - they'd circle the wagons and not speak to anyone except their little clique. But they were a small group and most of the authors there were approachable and delighted to talk to you. Invariably, they (the clique) always seemed to have something to do with organising or running it. Joe Abercrombie and Brent Weeks chatted to all and sundry at the last one I went to. I didn't like the scheduling - often you'd have to hurry across/up/down to get to the next talk you wanted to go to, because not enough time was scheduled for changeovers.
I loved the bookstands - you never get that amount of SciFi and Fantasy in one room outside of conventions, ever. Ooh, I liked the goody bags of giveaways, too.
If I were you, I'd start out at the smaller ones - better value for money, IMHO, and you'll find people exactly like you, who you'll bump into at the next one, and the next...